We have completed ventilatory chemoreceptor studies of 5 sets of parents of near-miss (aborted) SIDS infants compared to 5 age matched control couples. The ventilatory response to CO2 breathing was similar in mothers and fathers of near-miss SIDS compared to controls. The ventilatory response to progressive hypoxia in males was similar in both groups; one of 5 fathers had no increase in ventilation even at PAO2 40 mmHg. As a group, mothers of near-miss SIDS responded poorly to hypoxia: the average response was 42% of that in controls and each mother's response was greater than l SD below the mean for controls. We have also investigated the frequency and duration of apnea during REM vs quiet sleep in 10 normal control infants compared to l0 infants born to parents who previously lost a baby from SIDS. Data were obtained from continuous 12 hour recordings at home performed at 2, 8, and 14 weeks post-natal age. Siblings of SIDS as a group had significantly (p equals less than .05) more spontaneous apnea of 5-9.9 sec duration during REM sleep. By 14 weeks of age, they could not be distinguished from normal controls. During quiet sleep, there were no group differences; however, 3/10 near-miss infants had markedly increased (16-27 x controls) numbers of apneic spells 5-9.9 and 10-11.9 sec duration. Again, by 14 weeks, there were no group or individual differences.